1. Field of the Invention
The present invention relates to spectrometers and more particularly to a novel type of on-chip spectrometer that combines features of Fabry-Perot (FP) spectrometers with those of grating spectrometers.
2. Brief Description of the Related Art
Integrated optical spectrometers, in particular on-chip spectrometers, have wide applications in sensing, spectral analysis, signal processing, etc. Fabry-Perot spectrometers use high finesse, tunable, optical resonators to sweep cavity resonance over the spectrum of the signal to be analyzed, and in that way map the spectral content of the signal to the time domain. Grating spectrometers, on the other hand, map the spectral content of the signal into the spatial domain using gratings.
On-chip spectrometers have been realized using super-prism effects with a diffraction compensation and negative refraction. See, Momeni, B., et al., “Integrated photonic crystal spectrometers for sensing applications,” Optics Communications, 282(15): p. 3168-3171 (2009). Nevertheless, super-prism based spectrometers are not able to provide complete separation of the adjacent wavelength channels. On-chip spectrometers have also been realized with micro-ring resonators (as wavelength separators) and combined with an on-chip planar diffraction grating that couples the spectrally resolved output signal to a waveguide array, with large insertion loss (˜20 dB) due to scattering from the Fresnel lens. See, Kyotoku, B. B. C., L. Chen, and M. Lipson, “Sub-nm resolution cavity enhanced microspectrometer,” Optics Express, 18(1): p. 102-107 (2010).